IRS13 Word-Word Associations in Document Retrieval Systems chapter M. E. Lesk Harvard University Gerard Salton Use, reproduction, or publication, in whole or in part, is permitted for any purpose of the United States Government. IX-42 Request improved by association over null Request not improved by association over null Request improved by thesaurus over 15 9 24 null Request not improved by 10 8 18 thesaurus 25 17 42 a) Improvements of Association Methods over Null and Thesaurus Request Greatly Request not greatly improved (rank improved by associ- recall up by .1) ation over null by association over null Request greatly improved (rank recall up by .1) 5 3 8 by thesaurus over null Request not greatiy improved by thes- 9 25 34 aurus over null 14 28 42 b) Large Improvements of Association Methods over Null and Thesaurus Contingency Table for Co-Variation of Thesaurus and Association Methods Table 12